Hi, from 11 December 2022 like every second Sunday in December in Europe there is the timetable change for trains.
The new timetable is getting online on the websites of the train operators, but some trains are missing. Eurail.com has not yet the new timetable.
EC:
In your case, should be possible to book the EC 52 Milano C.le - Spiez, but the timetable for the train is missing. Maybe works on the rail line, and they are waiting with the timetable changes due to works? You could also take local trains RE to Domodossola and change there on RE direction Brig or Bern and exit in Spiez. On local trains reservation is not needed. I would check the timetable 2-3 weeks before, if the local trains will have busses instead or something similar due to works or have the Italian train company Trenitalia only forget to put to timetable online. Check it every week for new timetables. If you see something new and you have questions, ask us here in the community. On top I will give you the information that italian trains and trains Italy-Switzerland are possible to book the reservation via ÖBB instead of eurail.com. Check how it works here:
TGV:
In your case I would wait for the timetable of the TGV, till eurail.com can sell it, or you take from Basel a TER to Mulhouse or Strasbourg and get there on the TGV to Paris. From there you pay only 10 EUR or 20 EUR and it is possible to book it now via travel.b-europe (+4 EUR booking fee) instead of waiting for eurail.com. TER local train is the reservation not needed.